The present invention relates to a variable valve timing apparatus for a vehicle engine, and more particularly to a variable valve timing apparatus for a vehicle engine adapted to reduce the number of oil chambers and seals for maintaining tightness in the oil chambers, and to reduce driving oil pressure.
Generally, engines can generate high output when the exchange action between the combustion gas and fuel-air mixture in the combustion chamber; that is, the infusion of fuel-air mixture and exhaust action of the combustion gas, is fully and swiftly effected. However, because the infused fuel-air mixture and discharged combustion gas each have a kinetic inertia, suction and discharge actions of fuel-air mixture and combustion gas cannot be optimally controlled in situations where the relative operation state of intake/exhaust valves is constantly fixed.
As a result of the above, modem-day vehicles variably control the valve timing to maintain an optimal suction/exhaust state such that operational efficiency of engine over an entire range can be improved. The variable valve timing apparatus for variably controlling a valve timing thus described is generally divided into a helical spline type and a vane type. The variable apparatus of the helical spline type has a disadvantage in that manufacturing cost is high due to use of helical gears and much oil is consumed for driving thereof. Thus, the recent tendency is that the use of the variable apparatus of the vane type is on the increase.
FIGS. 1 and 2 respectively illustrate an installed example of a variable valve timing apparatus of the vane type and a sectional view thereof. The variable apparatus 100 is comprised of a rotor 102 secured at a tip end of cam shaft 101 and formed at a peripheral surface thereof with a plurality of vanes 103, and a housing 105 having the built-in rotor 102 and formed at a peripheral surface thereof with a driving gear 106. Furthermore, the housing 105 is formed therein with a plurality of protruders 107, while the vane 103 is mounted with a seal 104 for contracting an inner circumferential surface of the housing 105, and oil chambers 108 and 109 are formed on both sides of the vane 103. Oil infused into the two oil chambers 108 and 109 through an oil control valve is controlled to adjust phases of vanes 103 relative to the housing 105, thereby adjusting phases of cam shaft 101 connected to the rotor 102, by which opening and closing time of the valve can be variably controlled.
However, there is a problem in the variable valve timing apparatus thus described in that a rotor usually formed with 3-4 vanes is used (although there are some variations according to products) and, as a result, the number of oil chambers formed at the housing is increased. Also the number of seals for maintaining airtightness of the oil chambers is increased such that the augmented number of seals gives rise to increase of contact surface between the rotor and the housing, resulting in subsequent gain in needed driving oil pressure.
The present invention provides a variable valve timing apparatus for a vehicle engine constructed to reduce the number of oil chambers and seals and to decrease the needed driving oil pressure.
In accordance with a preferred embodiment of the present invention, a variable valve timing apparatus for vehicle engine comprises, a rotor secured at a tip end of a cam shaft, a housing with the rotor rotatably mounted therein, and a piston mounted in the housing for rotating the rotor. The rotor is formed with two vanes, the vanes being positioned within rotary spaces formed at the housing. Oil pressure chambers are formed at a housing body between the rotary spaces, where the oil pressure chambers are inherently mounted with the pistons. Each piston is connected via a rod to the vane located in opposition thereto.
According to a further alternative embodiment of the invention, a timing apparatus for an engine cam shaft comprises a rotor, a housing, a piston and rod, and a timing gear. The rotor is mounted on the cam shaft. The housing surrounds the rotor and defines at least one oil chamber. The piston is disposed in the chamber, with the rod linked to the rotor. The timing gear is mounted with the housing and preferably may be formed integrally therewith around the periphery. Oil pressure in the chamber may be varied to rotate the rotor with respect to the housing, thereby changing the phase of the cam shaft timing. Preferably, the rotor includes at least two opposed vanes and the housing defines at least two oil chambers serving as pressure cylinders communicating with an oil pressure control. Each cylinder then includes a piston linked to a vane of the rotor.